It is well known that thin metallic and ceramic layers may be deposited upon a substrate by a technique known as "magnetron sputtering". By such methods, a metal layer may be sputtered in an argon atmosphere using a target of the material to be deposited, generally as a cathode in a standard RF sputtering apparatus.
More recently, sputtering techniques have been used in the production of integrated circuits which require rapid and economical metal deposition with very close tolerances. Sputtering is an especially useful tool for the application of films and coatings where uniformity and chemical purity is important. Manufacturing costs may be lowered by improving film uniformity and deposition rate in high speed production processes typically used in integrated circuit manufacturing. Materials of particular importance in the manufacture of integrated circuits are aluminum and aluminum alloys. Targets of aluminum and/or aluminum alloys are used for sputtering to produce an aluminum film or coating on a substrate.
Sputtering processes and apparatus are disclosed in Bergmann et al. U.S. Pat. No. 4,889,772 and 4,961,831; Shagun et al., U.S. Pat. No. 4,961,832; Shimamura et al., U.S. Pat. No. 4,963,239; Nobutani et al., U.S. Pat. No. 4,964,962; Arita, U.S. Pat. No. 4,964,968; Kusakabe et al., U.S. Pat. No. 4,964,969 and Hata, U.S. Pat. No. 4,971,674; and the references referred to therein; sputtering targets are discussed also in Fukasawa et al., U.S. Pat. No. 4,963,240 and 4,966,676; and Archut et al., U.S. Pat. No. 4,966,677. These disclosures of sputtering processes and apparatus as well as sputtering targets are expressly incorporated herein by reference.
Sputtering target assemblies are typically constructed with a target member supported on a backing member. The target member includes a target surface of material to be sputtered and the backing member is intended to hold the target member in place in a sputtering apparatus. Targets must be replaced from time-to-time as the target material is removed or eroded away. For some target designs, it is necessary to replace both the target member and the backing member when the need to replace the target arises.
Some proposals have been made to reduce the time required to replace a sputtered target and to reduce the cost of target replacement. One such proposal is by Fielder et al. which is described in U.S. Pat. No. 4,820,397. This approach involves a particular target assembly design; however this design appears that is difficult and expensive to manufacture.
Another problem which has arisen with respect to target assemblies is distortion which may occur during manufacture of the target assembly from the heat input into members being welded. Conventional methods of manufacturing target assemblies have included TIG welding, brazing, soldering with high temperature solder, and explosion-bonding of the target member to a backing assembly. These methods of bonding generally involve the use of a filler material.
A conventional target assembly design utilizes annular targets positioned within a fixed backing plate and typically retained in place by soldering or joining as described above. The sputtering targets are independently removable from the backing plates for replacement of targets. In general, however, where the sputtering target is physically joined to the backing plate, (i.e., by welding, roll cladding or explosive bonding), it is usually removable as a unit into and out of the sputtering system, thus requiring both the spent target and backing member to be discarded.
Annular targets are preferred to facilitate cooling and circulation of coolant to the target assembly. However, where the target and backing members are of dissimilar materials, problems can arise due to the materials different thermal expansion rates. The soldered joint can be adversely affected and result in premature failure of the target assemblies. Qamar et al. have disclosed in U.S. Pat. No. 5,009,765 an alternative method for interconnecting the target and backing members which is purported to have improved heat transfer capability. The method involves forming a recess at the interface of the target member and the backing member and filling the recess with suitable filler bonding material. The members are joined together by aluminum TIG welding at the recess. Unfortunately, conventional welding techniques are frequently accompanying by a large heat effected zone which can lead to distortion of the target assembly during manufacture. Moreover, such methods also require a high input of heat to the members being welded and the use of a filler material.